The only possible way to make this statement with confidence is never measuring the overhead of tasks and goroutines. Tasks are lighter than goroutines, especially memory-wise. Don't trust me? Write any sample code you consider representative. Try spawning one million tasks and then one million goroutines, look at memory consumption and execution time. Surely the results will be as you say, right?

Also, .NET has channels out of box and they are being used where they make sense (which turns out to be not for every second thing even if it's unidiomatic, something about hammer and things looking like a nail).

In general, I think you either never worked with .NET at all or never understood it beyond surface level impression, and rely solely on urban myths about the topic of this discussion. Because there is no other way to explain the abstract "bottleneck" you imagine nor thinking as if Golang's runtime isn't a work-stealing scheduler just like .NET's threadpool, which it is.